An arrhythmia is a disturbance in the normal rate, rhythm or conduction of the heartbeat. An atrial arrhythmia originates in the atria. Atrial tachycardia (AT), one form of atrial arrhythmia, is a condition in which the atria contract at a high rate, e.g., 100 or more beats per minute. Atrial fibrillation (AF), another form of atrial arrhythmia, is characterized by a chaotic and turbulent activation of atrial wall tissue. The number of depolarizations per minute during AF can exceed 400. In addition, the AF stimuli can occur in the refractory period of the surrounding atrial myocardium.
AT can lead to AF, which in turn can be life threatening. Tachycardia is also associated with other low cardiac output symptoms, such as fatigue. Many atrial tachycardias are episodic, marked by abrupt onset but also abrupt termination, but cause considerable patient distress. If untreated, AT can lead to other dangerous life-threatening conditions, such as the development of blood clots which can cause stroke and possibly death.
Treatment for tachycardia may include anti-tachycardia pacing (ATP) or cardioversion, in which a train of high rate pulses or one or more high energy pulses is delivered to the heart in an attempt to restore a more normal rhythm. ATP is typically effective in converting stable atrial tachycardias to normal rhythm, and is often delivered via an implanted device. In many cases, a sequence of increasingly aggressive ATP therapies are applied until an episode of AT is terminated. The implanted device can be configured to discontinue ATP and immediately apply cardioversion in the event the AT degrades into atrial AF.